Process for preparing cooked bacon having reduced levels of N-nitrosamines

ABSTRACT

A process for preparing cured bacon which, when cooked for consumption, contains substantially reduced levels of N-nitrosamines. The process comprises the steps of nitrite-curing, heat processing and slicing bacon bellies and then spraying or otherwise applying to the resulting slices, after completion of said-nitrite curing and before cooking, a treating solution containing liquid smoke.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of co-pending application Ser. No. 158,679, filed June 12, 1980, entitled "Process for Preparing Cooked Bacon Having Reduced Levels of N-Nitrosamines, now U.S. Pat. No. 4,315,948."

BACKGROUND OF THE INVENTION

This invention relates to a process for preparing bacon and, more particularly, to a process for preparing bacon which, when cooked, will have reduced levels of N-nitrosamines.

For many years it has been common practice to prepare cured bacon by treating green (uncured) bellies with a curing solution (hereinafter "pickle") and then smoking the cured bacon to impart a desirable flavor. A major component of the pickle is sodium nitrite which inhibits the germination of Clostridium botulinum spores, thus ensuring that the cured bacon will be free of the deadly toxin produced by this bacterium. In recent years, however, much controversy has surrounded the use of sodium nitrite because there have been allegations that residual nitrite from the pickle can react with organic amines present in various cured pork products to form carcinogenic nitrosamines. This problem is accentuated with bacon because nitrosamine formation is induced by the elevated temperatures encountered when the bacon is cooked for consumption; i.e., those exceeding 300° F.

Many approaches have been considered in seeking a remedy to this problem and proposed remedies have included eliminating nitrite from the pickle or reducing residual nitrite levels in the cured product. Neither of these approaches is particularly satisfactory, however, because there is presently no suitable substitute for nitrite, and because reducing nitrite levels could increase the likelihood that C. botulinum spores would grow in the cured bacon.

Our co-pending application Ser. No. 158,679, supra, describes an invention which is based on the discovery that cured bacon having substantially reduced levels of N-nitrosamines, when cooked, can be prepared by injecting whole green bellies with a curing solution containing nitrite and a specially modified liquid smoke, and thereafter processing the bellies to effect curing. In said invention the liquid smoke is used in concentration to provide 20 to 160 ppm phenolic constituents and 10 to 800 ppm carbonyl compounds based on the weight of the green bellies, the ratio of carbonyls to phenols being within the range of 0.5-5 to 1.

Bacon made in accordance with said invention contains reduced levels of N-nitrosamines, while at the same time the levels of residual nitrite present in the uncooked cured product remain relatively unaffected, thus ensuring that the germination of C. botulinum spores will be prevented. In addition, the flavor of the product when cooked for consumption is remarkably improved.

SUMMARY OF THE PRESENT INVENTION

The present invention is based on the discovery that substantially reduced levels of N-nitrosamines can be achieved if liquid smoke is applied at a later stage--namely, after the bacon bellies have been cured, heat processed, and sliced, but before cooking. For example, rather than incorporate the liquid smoke in the curing solution to be injected into the bellies, it is possible to apply the liquid smoke, by spraying, dipping or other equivalent means, to the surface of the bacon slices after leaving the slicing machine.

The process of the present invention therefore comprises the steps of nitrite-curing, heat processing and slicing bacon bellies and then applying to the resulting slices, before cooking, a treating solution containing a liquid smoke in concentration to provide 20 to 160 ppm phenols and 10 to 800 ppm carbonyl compounds, based upon the weight of the sliced bacon, the ratio of carbonyls to phenols being within the range of 0.5-5 to 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the practice of the present invention, we may use as starting material any nitrite-cured bacon which has been cured, processed and sliced according to standard procedures which are well-documented in the art. See for example U.S. Pat. No. 3,595,679.

Cured bacon is typically prepared by immersing whole green bellies in pickle for a prescribed period of time or by injecting the pickle directly into the green bellies. Commercial procedures most commonly involve injection of the bellies because the curing process can be rapidly and efficiently completed. When cured in this way a quantity of pickle usually constituting 8-15% of the weight of the meat is injected; thus for example, if a 7-kilogram bacon belly were pumped (i.e., injected) with pickle at a level of 10%, a quantity of 700 grams of pickle would be used. The pickle normally contains a number of ingredients in addition to sodium nitrite. These include buffering agents such as sodium tripolyphosphate to stabilize the nitrite, agents to facilitate curing such as sodium erythorbate or ascorbic acid, and sodium chloride.

Following the step of injecting or otherwise introducing the curing pickle, the bacon bellies are normally drained for a period of time, combed and hung on trees in the conventional smokehouse manner, and then placed in heated, smoke-laden currents of air in the smokehouse. The times, temperatures and other conditions utilized in conventional smokehouse processing are well documented in the art. For example, in one such conventional procedure, cured bacon bellies are placed in a smokehouse at a temperature of 140°-145° F. and are held there until the internal temperature of the meat reaches about 130°-132° F. which will ordinarily require four to five hours in an air-conditioned smokehouse. The temperature of the house is then lowered to about 130° F. and held for another eight hours until the bellies are properly finished.

It is to be noted that, although liquid smoke may be used as a source to provide the smoke-laden currents of air in the processing step just described, application of liquid smoke in this manner and at this stage of the process is not effective to bring about any significant reduction of N-nitrosamines when the bacon is cooked for consumption.

Following the smokehouse processing step, the bellies are chilled in the ordinary manner in a bacon chill freezer for a period of 24 to 48 hours until the internal temperature is in the neighborhood of 24°-26° F., and then the bellies are subjected to pressure in a molding box or machine of conventional design and operation, the purpose of this being to square up the slab so that the slices obtained in the subsequent slicing operation will be as uniform as possible. The bellies are then sliced on high speed, rotary blade slicing machines to provide bacon slices which normally have a thickness in the range of 0.08 to 0.125 in.

In the practice of the present invention, bacon slices which have been produced in any of the conventional industry procedures are treated by applying to their surfaces a specially modified liquid smoke. The application may be by spraying, atomizing, dipping or other like means.

In order to prevent discoloration in this topical application wherein liquid smoke is concentrated on the surface of the slices, it is necessary to use a liquid smoke which has relatively reduced levels of color-forming constituents. An appropriate treating solution may be prepared using Aro-Smoke, a product of Red Arrow Products Company having a carbonyl to phenol ratio of approximately 1.4 to 1.

An alternate treating solution may be prepared using the following procedure: An aqueous solution of wood smoke is prepared and refined by means well known in the art or, if so desired, a commercial aqueous wood smoke, such as Red Arrow's CharSol C-10, (which has a carbonyl to phenol ratio of 7.1 to 1) may be used as the starting solution. The pH of the solution is adjusted to ca 10-11 with an appropriate base, such as sodium hydroxide, and the mixture is extracted with diethyl ether to remove certain of the carbonyl-containing compounds. The aqueous solution is reacidified to a pH of ca 2-3 with an appropriate acid, such as hydrochloric acid, and the mixture is extracted with diethyl ether. After evaporation of the ether, a water-insoluble extract is obtained for which the ratio of carbonyl-containing compounds to phenolic constituents is in the range of 0.5-5 to 1. Preferably, this ratio will be in the range of 0.75-3 to 1.

If it is desired to use the above water-insoluble extract in an aqueous treating solution, it is preferable to include a food grade emulsifier. A wide range of emulsifiers is available and the effective amount of emulsifier required will depend on the characteristics displayed by each individual emulsifier. Polysorbate emulsifiers are generally satisfactory to practice the present invention, and polysorbate 80 is particularly preferred when not less than 0.2% of emulsifier is used, based on the weight of the solution. Certain other emulsifiers which provide suitable emulsification may also exhibit other characteristics which make them less desirable to use. Lecithin, for example, has been shown to increase N-nitrosopyrrolidine formation. Therefore, in view of the result which is to be achieved by utilizing the process of the present invention, emulsifiers which exhibit this tendency should be avoided.

The amount of the unique smoke flavoring composition which is added to the treating solution can vary depending on a number of factors, including the amount of treating solution that can be held on the surface of the bacon slices and the amount of smoke flavor that is desired for the cooked bacon. However, we have found that when liquid smoke having a carbonyl/phenol ratio of 0.5-5 to 1 is incorporated in the treating solution, and a quantity of solution is sprayed or otherwise applied to the bacon slices in concentration to provide 20-160 ppm of phenols and 10-800 ppm of carbonyls based on the weight of the meat, the objective of the present invention will be achieved. Preferably, the concentration range for the phenols will be 40-120 ppm and for the carbonyls will be 30-360 ppm.

A preferred way of applying the treating solution to the bacon slices is by spraying the solution on the surface of the slices as they leave the slicing machine and are carried on a conveyor belt to the weighing and packaging area. Any suitable equipment involving nozzles which provide atomization or spray application may be utilized. For example, a Preval sprayer unit, manufactured by Precision Valve Corporation, Yonkers, N.Y., is useful in the practice of the invention. Other means of application, such as dipping or immersing the slices in a bath of treating solution, are also contemplated by the invention.

It is of course essential that the bacon slices be treated with the liquid smoke prior to being exposed to temperatures as high as, or approaching, those involved in cooking the bacon for consumption. It is believed that the formation of N-nitrosamines is catalyzed by temperatures approaching 300° F. or higher, and if the application of liquid smoke, as in the present invention, is delayed until after the bacon slices have been subjected to such temperatures, either by frying or precooking, then significant quantities of N-nitrosamines may already have been formed prior to the smoke application, and the purpose of the invention may have been defeated.

An advantage of the present invention is that nitrites are used in the conventional manner and in the conventional quantities to cure and flavor the bacon and protect it against harmful organisms such as C. botulinum; and in addition the bacon contains substantially reduced levels of N-nitrosamines upon frying or cooking at high temperatures.

The following examples are illustrative of the practice of the invention. It will be understood of course that various modifications thereof can readily be evolved in view of the guiding principles and teachings provided herein.

EXAMPLE 1

A 200-ml quantity of CharSol C-10 was treated according to the procedure set forth above to give 8.4 g of oily extract. A 29% solution of the extract in polysorbate 80 was prepared and the phenolic- and carbonyl compound constituents of this smoke ("Prepared Smoke" as used in this Example) were assayed spectrophotometrically using 2,6-dimethoxyphenol and 2-butanone as the standards, respectively. From the assay results the carbonyl/phenol ratio was determined. Similar assays and ratio calculations were also made for Aro-Smoke (which contained ca 80% polysorbate), CharSol C-10, and Royal Smoke, another commercial aqueous liquid smoke from Griffith Laboratories. The following results were obtained.

    ______________________________________                                                    Phenols  Carbonyls Ratio                                            Sample     (mg/ml)  (mg/ml)   Carbonyls:Phenols                                ______________________________________                                         Prepared Smoke                                                                            35       54        1.5:1                                            Aro-Smoke  39       54        1.4:1                                            Royal Smoke                                                                               7.5      79        10.5:1                                           CharSol C-10                                                                              14       99        7.1:1                                            ______________________________________                                    

EXAMPLE 2

The following test results demonstrate that application of liquid smoke to the external surfaces of whole bellies during smokehouse processing has no significant effect in the reduction of N-nitrosamines in the cooked or fried bacon.

Twenty-four green skin-on bacon bellies were obtained, divided into two groups of 12, and skinned prior to processing. Both groups were pumped at levels of 13%, based on the weight of the bellies, with the following curing pickle:

    ______________________________________                                         Ingredient            Percentage                                               ______________________________________                                         Water                 85.64                                                    Sodium Chloride       12.50                                                    Sodium Tripolyphosphate                                                                              1.25                                                     Sodium Erythorbate Monohydrate                                                                       0.50                                                     Sodium Nitrite        0.10                                                     Veralock (a flavoring material)                                                                      0.01                                                     ______________________________________                                    

Both groups (Group A and Group B) were heat processed under identical conditions to cure the bacon, and the bellies in Group B were also externally smoked with atomized CharSol C-10 at ca five times the amount of liquid smoke normally employed in commercially produced bacon. The bellies were then chilled and two days later approximately 1-pound center drafts containing ca 17-18 slices per draft were taken from each belly.

Five days after slicing, bacon samples from each group were fried at 340° F. for three minutes per side, and the fried bacon was analyzed for N-nitrosamine content using N-nitrosopyrrolidine as the standard. The following results were obtained.

    ______________________________________                                                          N--Nitroso-                                                   Group            pyrrolidine (ppb)*                                            ______________________________________                                         A. No external smoke                                                                            14 ± 5                                                     B. External smoke                                                                               16 ± 3                                                     ______________________________________                                          *Data represents the mean ± the standard deviation from N = 16              different determination.                                                 

EXAMPLE 3

Twelve skin-on bellies having green weights averaging 18 to 20 pounds were processed in a commercial packing plant according to USDA approved procedures. The processing involved injecting the bellies with a conventional curing pickle containing approximately 120 ppm sodium nitrite; combing and draining; processing in a smokehouse to an internal temperature of approximately 136°-140° F.; tempering; chilling; molding; and finally slicing and putting up in drafts consisting of approximately 500 grams of bacon, totaling 17 to 18 slices per draft, the average thickness of each slice being approximately 0.09 in.

Two of the center drafts from each of the 12 bellies were selected for testing, as follows:

    ______________________________________                                         No. 1 Drafts                                                                             Received no treatment                                                (Control)                                                                      No. 2 Drafts                                                                             The slices in these drafts were sprayed with                         (Aro-Smoke)                                                                              5.0 grams of an aqueous solution containing                                    approximately 1 gram Aro-Smoke (2,000 ppm                                      Aro-Smoke based on the weight of the bacon)                          ______________________________________                                    

After the above spray application, the drafts were vacuum packaged, stored for 6 days at 36°-40° F., and then fried and analyzed. In the analysis for N-nitrosamines, 12 samples from each type of draft (24 total samples) were fried 3 minutes on each side in a pre-heated fry pan at 340° F.±10° F. After blotting the fried bacon slices with paper toweling (to remove excess fat), nitrosamine values were determined by Thermal Energy Analyzer (T.E.A.) methodology, following the procedures set forth in Fine et al, Anal. Chem., 47, 1183 (1975). The results are set forth as follows:

    ______________________________________                                                                 % Reduction of                                                   N--Nitroso-   N--Nitrosopyrrolidine                                  Treatment pyrrolodine (ppb)*                                                                           Compared to Control                                    ______________________________________                                         No. 1 Drafts                                                                             29.9          --                                                     (Control)                                                                      No. 2 Drafts                                                                             16.8          43.8                                                   (Aro-Smoke)                                                                    ______________________________________                                          *Average of 12 different samples                                          

We claim:
 1. A process for preparing cured bacon which, when cooked for consumption, contains substantially reduced levels of N-nitrosamines, said process comprising the steps of nitrite-curing, heat processing and slicing bacon bellies and then applying to the external surfaces of the resulting slices, after completion of said nitrite-curing and before cooking, a liquid smoke in concentration to provide 20 to 160 ppm phenols and 10 to 800 ppm carbonyl compounds, based upon the weight of the sliced bacon, the ratio of carbonyls to phenols being within the range of 0.5-5 to
 1. 2. The process of claim 1 in which the liquid smoke is applied in a treating solution which also contains an effective amount of a food grade emulsifier which does not substantially increase N-nitrosamine formation.
 3. The process of claim 2 in which the said food grade emulsifier is a polysorbate emulsifier.
 4. The process of claim 2 wherein said treating solution is sprayed on the surface of said bacon slices.
 5. The process of claim 1 in which the ratio of carbonyl to phenolic compounds is within the range of 0.75-3 to
 1. 6. The process of claim 5 in which the said liquid smoke is in concentration to provide 40 to 120 ppm of phenols and 30 to 360 ppm of carbonyls based upon the weight of the sliced bacon. 